Bearing arrangement for a centrifugal casting machine

ABSTRACT

A bearing arrangement for a centrifugation injection mold, comprising an upper mold portion ( 10 ) and a lower mold portion ( 20 ), which are respectively and rotatively mounted to an upper bearing ( 30 ) and to a lower bearing ( 40 ), the latter comprising: a first flat ring ( 41 ) affixed to a machine structure (E) and presenting a radial gap that is internal in relation to the lower mold portion ( 20 ); an annular cage ( 42 ) bearing spheres ( 44 ) seated on the first flat ring ( 41 ), said annular cage ( 42 ) presenting radial gaps that are external and internal in relation to the machine structure (E) and to the lower mold portion ( 20 ), respectively; and a second flat ring ( 45 ) inferiorly seated on the spheres ( 44 ) of the annular cage ( 42 ) and maintaining radial gaps that are external and internal in relation to the machine structure (E) and to the lower mold portion ( 20 ), respectively, axially bearing the latter. The lower mold portion ( 20 ) incorporates an annular conical seat ( 25 ) on which is seated, when the mold (M) is taken to the closed position, an annular conical guide ( 15 ) incorporated to the upper mold portion ( 10 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 of PCT/BR02/00177 filed on Dec. 9, 2002.

FIELD OF THE INVENTION

The present invention refers to a bearing arrangement for two-piecemolds used in the centrifugation injection of the cage made of aluminumor other adequate material into the stack of steel laminations of anelectric motor rotor, particularly the rotor of small electric motors,such as those used in the hermetic compressors of small refrigerationsystems.

BACKGROUND OF THE INVENTION

It is already known from the prior art the injection effected bycentrifugation of the aluminum cages in rotors, which are formed by astack of overlapped annular steel laminations provided with openingsthat are longitudinally aligned with the openings of the otherlaminations of the stack, in order to define a plurality of axialchannels interconnecting the external faces of the end laminations ofthe stack and which are angularly spaced from each other along acircular alignment, which is concentric to the longitudinal axis of thelamination stack, but radially spaced back in relation to the lateralface of the latter.

The lamination stack, with its longitudinal axis vertically disposed, ispositioned in the interior of a mold that defines a lower annular cavityclose to the external face of the lower end lamination, and an uppercavity, which is substantially cylindrical or frusto-conical, close tothe external face of the upper end lamination and opened to a channelfor the entry of aluminum into the mold.

During the aluminum pouring, the lamination stack has its central axialbore, in which will be later mounted the shaft of the electric motor,filled with a core, which has an upper end substantially leveled withthe upper end lamination the lamination loan and stack, and a widenedupper end lower portion, which is seated on a respective lower endwidening of the central axial hole of the lamination stack and againstthe mold portion that defines the lower cavity.

The aluminum is poured into the lower cavity, passing through the axialchannels of the lamination stack to the lower cavity, filling thelatter, the axial channels, and the upper cavity, in this order, andsolidifying in a radial inward upward pattern, as the mold rotatesaround its vertical axis and the metal cools.

Upon completion of the aluminum pouring and solidification, the mold isopened and the formed rotor is submitted to one or more operations toeliminate the inlet channel and unobstruct the adjacent end of thecentral axial bore of the lamination stack, and to define the correctinner profile for the upper ring of the aluminum cage, which furthercomprises a single piece lower ring, which is already formed by themold, and a plurality of bars formed in the interior of the axialchannels of the lamination stack.

In the centrifugation injection of these rotors, the upper and lowercavities of the mold and the lamination stack itself are heated, so thatthe aluminum passes through the upper cavity and through the axialchannels of the lamination stack without solidifying, gravitationallyreaching the lower cavity, filling it and beginning to solidify, fromthe outside to the inside and from the bottom upwardly, as the moldrotates.

In order that the injection mold involving and locking superiorly andinferiorly the lamination stack can rotate around its verticallongitudinal axis, the upper and lower cavities of the mold are mounted,respectively, onto an upper bearing and a lower bearing that are carriedby the structure of the injection equipment.

In the bearing arrangements of the type mentioned above, the occurrenceof deviations of concentricity and parallelism between the axes of theupper and lower cavities cause vibrations in both the mold and thelamination stack during rotation of the mold, which vibrations act onthe metallic material being solidified in the upper and lower cavities.

A major problem caused by said vibrations of the rotating mold duringthe solidification of the aluminum, is that the bars of the cage, whichare formed in the interior of the axial channels of the laminationstack, and even the rings tend to present cracks, the bars beingtransversally broken inside the lamination stack in a way notperceptible by an external visual checking of the finished rotor. Thebreakage or crack of one or more bars, or of the upper or lower rings ofthe cage will considerably impair the quality of the rotor andconsequently the efficiency of the electric motor to be formed.

One of the possibilities to minimize or even eliminate the loss ofquality by undue vibrations of the mold during the aluminumsolidification is to mount both cavities of the mold to only one lowerbearing, whereby the shafts of both parts of the mold are unified.However, in this solution, the upper and lower cavities of the mold areguided by columns that are affixed to the lower cavity. The upper cavityis axially displaceable, guided by the columns, to open and close themold, whereby the upper cavity is slidingly retained in the columns,considerably limiting the automation of the operations of feeding thelamination stack in the mold, and also the removal of the centrifugedrotor, besides the problems of concentricity and rotor strike.

OBJECTS OF THE INVENTION

Aiming at solving the deficiencies of the bearing arrangements forcentrifugation injection molds proposed by the prior art, the presentinvention proposes a bearing arrangement of relatively simpleconstruction, which is efficient to assure the balanced rotation of themold during the solidification of the cage in the lamination stack,avoiding vibrations and rupture of the component parts of the cage,particularly the bars thereof, and substantially minimizing the problemsof concentricity and rotor strike.

It is a more specific object of the present invention to provide abearing arrangement, such as mentioned above, which presents the upperand lower cavities of the mold rotatively mounted to respectivebearings.

SUMMARY OF THE INVENTION

The bearing arrangement of the present invention is applied to acentrifugation injection mold of aluminum or other metallic alloy, whichis adequate to form several parts, such as for example, the cage of anelectric motor rotor used in hermetic compressors.

The injection mold is of the type that comprises an upper mold portionand a lower mold portion, which are axially displaceable between an openmold position and a closed mold position and respectively and rotativelymounted to an upper bearing and to a lower bearing that are affixed to amachine structure for centrifugation injection.

According to the invention, the lower bearing comprises: a first flatring affixed to the machine structure, orthogonally to the axis of thelower mold portion, and presenting a radial gap that is internal inrelation to the lower mold portion; an annular cage having axial throughhousings bearing respective spheres seated on the first flat ring, saidannular cage presenting radial gaps, which are external and internal inrelation to the machine structure and to the lower mold portion,respectively; and a second flat ring, which is inferiorly seated on thespheres of the annular cage immediately below, in order to axially bearthe lower mold portion, and which presents radial gaps, which areexternal and internal in relation to the machine structure and to thelower mold portion, respectively.

This constructive arrangement allows for a certain relative radialdisplacement between the lower mold portion and the machine structure,with the annular cage of spheres being free to radially adjust itselfbetween two consecutive flat rings.

Thus, the lower mold portion can be displaced so that its axis bealigned with the axis of the upper mold portion.

In order to bring the lower mold portion to an operative positionaligned with the upper mold portion, the former incorporates an annularupper conical seat, which is orthogonal and concentric to its axis andon which is seated, when the mold is taken to the closed position, anannular conical guide incorporated to the upper mold portionorthogonally and concentrically to the axis of the upper mold portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below, with reference to the encloseddrawings, in which:

FIG. 1 is a simplified diametrical vertical sectional view of aninjection mold in the closed condition and using the bearing arrangementof the present invention;

FIG. 2 is an enlarged diametrical sectional view of the self-aligninglower bearing used in the mold illustrated in FIG. 1; and

FIG. 3 is an enlarged view of part of the mold illustrated in FIG. 1,showing the seating of the annular conical guide against the annularconical seat.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

The figures of the enclosed drawings illustrate the bearing arrangementapplied to a centrifugation injection mold of an aluminum cage, which isincorporated into a lamination stack of an electric motor rotor, whoseconstruction is well known in the prior art. However, it should beunderstood that the present bearing arrangement can be applied to moldsfor the centrifugation injection of other parts that can be negativelyaffected by the disalignment between the mold parts during thesolidification of the heat injected metal.

The illustrated mold M comprises an upper mold portion 10, and a lowermold portion 20, which are relatively and axially displaceable betweenpositions of the upper mold 10 defining an upper cavity 11 andincorporating an upper tubular projection 12 for liquid metal supply. Inorder to be able to rotate around its axis during the centrifugation ofthe liquid metal in the solidification phase inside the mold M, theupper mold portion 10 is mounted to a support S of a centrifugationinjection machine by means of an upper bearing 30 comprising two rollingbearings.

The lower mold portion 20 defines a lower cavity 21 to be operativelyassociated with the upper cavity 11, upon the closing of the mold M inorder to define the plenum that will be filled with the liquid metal. Inthe illustrated example, both mold cavities are respectively associatedwith the two opposite end faces of a lamination stack L of a rotor to beformed.

The lower mold portion 20 is mounted to the machine structure E by meansof a lower bearing 40 that presents self-aligning characteristics, aswill be described ahead.

In the illustrated construction, the lower cavity is formed by a lowermold block 22 seated on springs 23 carried by the lower mold portion 20,allowing the latter to be resiliently compressed against the upper moldportion 10.

According to the invention, the lower bearing 40 comprises a first flatring 41 usually made of steel, which is affixed to the machine structureE, in a position orthogonal to the axis of the lower mold portion 20 andpresenting a certain radial gap that is internal in relation to theadjacent surface of the lower mold portion 20, allowing the latter to beradially displaced in any direction, by an extension sufficient to annulthe disalignments between the axis of both portions of the mold M.

On the first plane 41 is mounted an annular cage 42, in the form of aflat ring, which is provided with two concentric circular alignments ofaxial through housings 43 which will retain and bear respective spheres44 with a diameter that is greater than the thickness of the cage, andwhich seat on the first flat ring 41. The annular cage 42 is dimensionedto present radial gaps, which are external and internal in relation tothe machine structure E and to the lower mold portion 20, respectively.Thus, the annular cage 42 can be radially and relatively displaced overthe flat ring 41, upon the relative radial displacements between thelower mold portion 20 and the machine structure E in the self-aligningprocess of both mold portions. It should be understood that the annularcage 42 might present one, two or more concentric circular or helicalalignments of the axial through housings 43.

The lower bearing 40 further comprises a second flat ring 45 presentingradial gaps, which are external and internal in relation to the machinestructure E and to the lower mold portion 20, respectively, in aposition that is orthogonal and concentric in relation to the axis ofthe lower mold portion 20, in order to be seated on the spheres 44 ofthe annular cage 42 immediately below, axially bearing the lower moldportion 20.

The external and internal radial gaps of the second flat ring 45 allowthe latter to be radially displaced, while it is seated on the spheres44, in order to bring the axes of the mold portions to an alignedcondition. In order that both portions of the mold M be conducted to analignment condition of their axes, the lower mold portion 20incorporates an annular conical seat 25, which is orthogonal andconcentric to the axis of the lower mold portion 20, and against whichis seated, when the mold M is conducted to the closed position, anannular conical guide 15 that is incorporated to the upper mold portionorthogonally and concentrically to the axis of the latter.

The closing of the mold M by the direct or indirect mutual seating ofthe upper mold portion 10 and lower mold portion 20 occurs before theseating of the annular conical guide on the annular conical seat 25,since the springs 23 that sustain the lower mold block 22 are compresseduntil the end of the approximation of the parts and the axial geometricalignment thereof by actuation of the two cooperating annular conicalsurfaces.

In the illustrated embodiment, on the second flat ring 45 is seated onemore pair of bearings formed by another annular cage 46, which is equalto the first one and onto which is seated another flat ring 47internally affixed to the lower mold portion 20 and presenting a radialgap that is external in relation to the machine structure E. It shouldbe understood that the invention is not limited to two pairs ofbearings, which are each defined by an annular cage and an upper flatring affixed to the lower mold portion, and which are inferiorly seatedon a first flat ring affixed to the machine structure.

1. A bearing arrangement for a centrifugation injection mold, comprisingan upper mold portion and a lower mold portion, which are relatively andaxially displaceable between an open mold position and a closed moldposition, and which are respectively and rotatively mounted to an upperbearing and to a lower bearing that are affixed to a machine structurefor the centrifugation injection, characterized in that the lowerbearing comprises: a first flat ring affixed to the machine structureorthogonally to the axis of the lower mold portion and presenting aradial gap that is internal in relation to the lower mold portionwherein the lower mold portion is positioned above the machine structuresuch that the machine structure defines the outer surfaces of the radialgap and the lower mold portion defines the inner surfaces of the radialgap and wherein the first flat ring is positioned within the radial gapdefined by the lower mold portion and the machine structure and iscoaxial with the axis of the lower mold portion; an annular cagecontaining at least one circular alignment of axial through housingsbearing respective spheres, and seated on the first flat ring coaxialwith the first flat ring, said annular cage presenting radial gaps,which are external in relation to the machine structure and internal inrelation to the lower mold portion; and a second flat ring seated on thespheres of the annular cage immediately below and coaxial with theannular cage, in order to axially bear the lower mold portion, and whichpresents radial gaps that are external in relation to the machinestructure and internal in relation to the lower mold portion the lowermold portion incorporating an annular conical seat, which is orthogonaland concentric to the axis of said lower mold portion and on which isseated, when the mold is conducted to the closed position, an annularconical guide that is incorporated to the upper mold portionorthogonally and concentrically to the axis of said upper mold portion.2. The bearing arrangement as set forth in claim 1, wherein the annularcage is in the form of a flat ring with a thickness inferior to thediameter of the spheres.
 3. The bearing arrangement as set forth inclaim 2, further comprising at least one additional bearing assemblyformed by another annular cage carrying another flat ring internallyaffixed to the lower mold portion and presenting a radial gap that isexternal in relation to the machine structure, each additional bearingassembly being seated on a bearing assembly immediately below, with thelowermost bearing assembly being defined by the second flat ring and bythe lower annular cage seated on the first flat ring.
 4. The bearingarrangement as set forth in claim 3, wherein the annular cages of eachbearing assembly are equal to each other.
 5. The bearing arrangement asset forth in claim 1, wherein the annular cage has two concentriccircular or helical alignments of housings.
 6. The bearing arrangementas set forth in claim 5, further comprising at least one additionalbearing assembly formed by another annular cage carrying another flatring internally affixed to the lower mold portion and presenting aradial gap that is external in relation to the machine structure, eachadditional bearing assembly being seated on a bearing assemblyimmediately below, with the lowermost bearing assembly being defined bythe second flat ring and by the lower annular cage seated on the firstflat ring.
 7. The bearing arrangement as set forth in claim 6, whereinthe annular cages of each bearing assembly are equal to each other. 8.The bearing arrangement as set forth in claim 1, further comprising atleast one additional bearing assembly formed by another annular cagecarrying another flat ring internally affixed to the lower mold portionand presenting a radial gap that is external in relation to the machinestructure, each additional bearing assembly being seated on a bearingassembly immediately below, with the lowermost bearing assembly beingdefined by the second flat ring and by the lower annular cage seated onthe first flat ring.
 9. The bearing arrangement as set forth in claim 8,wherein the annular cages of each bearing assembly are equal to eachother.